El basamento metamórfico de la Sierra de Quilmes, República Argentina

TOSELLI, A.J.; ROSSI DE TOSELLI, J.; RAPELA, C.W.

Revista Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 1978 vol. 33 p. 105 - 121

0004-4822

Several petrographical and petrographical features of the Sierra de Quilmes (Pampean Ranges, Argentina) are here described. Within the metamorphic basement two units called Agua del Sapo Complex and Tolombón Complex were recognized. The Agua del Sapo Complex is represented by a secuence of progressive metamorphism ranging from schist to gneisses with diagnostic paragenesis of low grade, (Almandine Kyanite) medium grade and (almandine) high grade (Winkler, 1967). The Tolombón Complex was identified in three zones named northern southern and western, respectively. The metamorphic grade increases towards the west in the northern and southern zones. Two lithologic groups were recognized: one composed of quartzites, schists gneisses and smaller amounts of hornblende-norites and hyperstenes granulites and the other made up of migmatites regionally developed in the northern zone. Cordierite is invariably present iii rocks of medium and high grades of the three zones. Nevertheless, certain differences between zones were founded, thus while the sequence of metamorphic grades in the northern zone was (Cordierite + Almandine) medium grade (Cordierite + Almandine) high grade and also (Granolite) high grade, in the southern one low grade and (Cordierite) high grade were present. Temperatures and pressures were calculated using the thermodinamic method developed by Currie (1971) for coexistent garnets and cordierites. The infered P, T gradients clearly shown that the differences between complexes are due not only to pressures, but temperatures of high grade zones of Tolombón Complex were considerably higher than the ones corresponding to the Agua del Sapo Complex.